The Notch signaling pathway is known to play a key role in establishing cell fate in animal development, including in the developing vertebrate nervous. The mechanism by which Notch regulates cell fate has been shown to require a core pathway of signaling components, including membrane bound ligands that bind to the Notch receptors, reading to the activation of Notch target genes via the DNA binding protein Su(H). A major unanswered question is how the output of this core signaling pathway is regulated in order for the Notch pathway to have such a diverse range of action. Using Xenopus embryos as a model system for studying gene function during vertebrate neural development, the proposed experiments will determine the role of two new genes, which appear to regulate Notch signaling. In addition, a battery of Notch target genes have been identified, and the proposed experiments will analyze the mechanisms that control their expression. These experiments will provide significant insight into the mechanisms by which cell fate is controlled by the Notch pathway during vertebrate neural development. In addition, these insights may provide a means to treat human disease which are caused by mutations in the Notch pathway, including CADASIL and Alagille syndromes.